<!DOCTYPE html>
<html>
  <body>
    <style>
      #a { border: 1px solid black; width: 100px; height: 100px; left: 10px; }
      #b { border: 1px solid blue; width: 50px; height: 50px; left: 20px; }
      div { position: absolute; }
    </style>
    <div id="a">
      <div id="b">
      </div>
    </div>
  </body>
</html>

